1. Field of the Invention
The invention relates to ankle replacement systems including designs, methods and apparatus that reduce and/or prevent problems associated with subsidence, loosening, and late infection, in part, by incorporating a novel surgical procedure for replacing an ankle, at least in part, through a tibial tubercle exposure. The present invention is also directed to novel surgical instruments useful for performing an ankle replacement procedure.
2. Description of the Background
Until the early to mid 1970""s, patients with injured or diseased ankle joints commonly resulting from rheumatism, or degenerative or traumatic arthritis, had few options when their ankle joints failed. The most common procedure to help these patients regain some use of their ankle was obliteration of the joint by fusion, a procedure that is still commonly used today. Fusion, however, rendered the ankle stiff and generally immobile relative to the lower leg, resulting in limited use and additional stresses on the knee and hip joints.
Probably the first reported use of total ankle prosthesis was by Buckholz in 1969. The medical community recognized that such ankle replacement led to largely increased use of the ankle joint because the replacement permitted ankle ranges of motion which generally attempted to mimic the natural human joint. Since that time, ankle replacement prostheses have become increasingly common in use and improved in design.
An early ankle replacement prosthesis, disclosed in U.S. Pat. No. 3,886,599, incorporated herein by reference, consisted of an articulated two-part prosthesis having a convex-to-convex bearing surface provided by an upper metallic portion and a lower portion formed of high density polyethylene. The upper metallic portion had a stem adapted for engagement with a prepared distal end of the tibia, and the lower portion had a shank adapted for engagement with and connection to a prepared surface of the talus.
Another early ankle replacement prosthesis, disclosed in U.S. Pat. No. 4,069,518, incorporated herein by reference, comprised a talar member with three adjacent longitudinally and laterally convexly shaped bearing surfaces with a means for attaching the talar member to the talus; and a tibial member with three complementary longitudinally and laterally concavely shaped bearing surfaces with a means for attaching the tibial member to the tibia.
Although these types of ankle replacements had some initial success in helping patients regain use of their ankle joint, the long range prognosis for patients has not been good. For example, by the mid 1980""s, long term follow-ups were reported for patients who had received these types of ankle replacements in the early to mid 1970""s. At a follow-up of five years, failure rates were reported to be from 35% to 76% in ankle arthroplasties. Failures have been found in all models of total ankle replacement including the Mayo Clinic Total Ankle, the Oregon, and the Beck-Steffee models. See Kitaoka, H. B. et al., Clinical Results of the Mayo Total Ankle Arthroplasty, J. Bone Joint Surg. Am., 1996; see also Wynn, A. H. et al., Long-term follow-up of the Conaxial (Beck-Steffee) Total Ankle Arthroplasty, Foot Ankle, 1992. Complications included aseptic loosening, delayed wound healing, wound dehiscence, and prosthetic subsidence.
Another ankle replacement device was described in a similar time period in U.S. Pat. No. 4,232,404, incorporated herein by reference. This prosthesis comprises a talar component with a convex articulatory surface that has an intermediate part-circular-cylindrical area coaxially flanked at each end by similar mutually divergent part-conical areas. The prosthesis also has a tibial component with an asymmetrical concave articulatory surface complimentary with the convex cylindrical area and one of the conical areas of the talar component. Additionally, this device has a fibular component which has an articulatory surface engaged with the other conical areas.
A similar device with tibial, fibular, and talar members has been in use since 1984 under the name AGILITY(trademark) Ankle by DePuy of Warsaw, Ind. In 1997, outcomes of the first 100 total ankle arthroplasties using the AGILITY(trademark) Ankle were reported by Dr. Frank G. Alvine, who had performed all 100 surgeries between 1984 and 1993. Approximately 61% of the replacements were reported as successful syndesmosis fusions, while the remaining cases evidenced various problems from delayed unions and nonunions which were often associated with the development of ballooning and circumferential lysis at the tibial component. See Orthopaedics Today, Jul. 7, 1997, pp. 16-17. The AGILITY(trademark) Ankle takes advantage of tibiofibular sydesmosis for increased contact and better force distribution than the previous ankle replacements that relied on stability from connections to the talus and tibia. However, the tibiofibular syndesmosis is a large contributing factor in loosening and ballooning osteolysis problems encountered with the AGILITY(trademark) Ankle.
A more current ankle replacement device is described in U.S. Pat. No. 5,766,259, incorporated herein by reference. This prosthesis also comprises tibial, talar, and fibular components. A floating bearing is located between the tibial and talar prosthesis components. The floating bearing makes full contact with the talar component and is capable of limited mediallateral and fore and aft movement with the tibial component. The fibular component has a plastic insert which cooperates with the talar and tibial components to provide stability to the ankle joint.
A common element between the previous ankle replacement systems, the AGILITY(trademark) Ankle and the system described in U.S. Pat. No. 5,766,259 is that they all comprise a talar member, fixed to the talus, as one of their main functioning components. The talus, however, is relatively small, providing a small area of bone for fixation. Also, in most of these ankle replacement systems, the talar component is cemented to the talus. The combination of fixation with bone cement to a small fixation area allows for erosion of the cement from the fixation area and an increase in compliance due to formation of a soft tissue capsule over time. This contributes to aseptic loosening and migration of the device. Furthermore, although more recent replacements have attempted to alleviate stress from the tibia and talus by incorporating a fibular component and infusing tibiofibular syndesmosis, they still face common problems of prosthesis migration and loosening, and osteolysis at the tibial component.
Another common element between these previous systems is that they are installed through incisions made at or near the ankle. Such surgical procedures require making large incisions at the ankle, moving the tendons and other soft tissue aside, and separating the tibia and fibula from the talusxe2x80x94essentially detaching the foot from the legxe2x80x94to install the device, subsequently requiring complicated realignment and reattachment of the foot. In addition, these devices typically incorporate a relatively short tibial component to simplify installation. These procedures commonly result in infection and extended healing time with possible replacement failure from improper realignment. The surgery also has increased risks associated with cutting or damaging neighboring nerves and tendons which may lead to further complications.
There is, therefore, a need in the field for a total ankle replacement system that reduces the occurrence of subsidence and aseptic loosening while retaining the majority of the foot""s natural motion. There is also a need for a less invasive surgical method to install such a device to provide improved healing and a decreased failure rate.
The present invention overcomes the problems and disadvantages associated with current strategies and systems in total ankle replacement (TAR). In particular, the present inventive ankle replacement method and system is designed to prevent subsidence and aseptic loosening, problems common to the TAR devices currently in use. This device allows fixation of the lower prosthesis body to the calcaneus and/or the talus, thereby significantly increasing the bone available for fixation. The enlarged available bone base allows fixation of larger trays and prosthetic bases and allows for anchoring of the lower prosthesis body with screws or other fixation methods not possible with fixation to only the talus. This prosthesis system provides greater stability and stress absorption for the prosthetic ankle joint, and decreases the probability of prosthesis loosening and subsidence.
In one embodiment, the novel ankle replacement prosthesis comprises a member that is attached to the calcaneus. In another embodiment, the novel ankle replacement prosthesis comprises a lower member which is attached to both the talus and calcaneus in such a way as to fuse the talus to the calcaneus. In yet another embodiment, the novel ankle replacement prosthesis comprises a lower member that is attached to both the talus and the calcaneus, but which allows some relative movement between the talus and calcaneus, thereby closely mimicking the natural movement of the human foot. Said lower member could comprise a stem which incorporates a joint allowing relative movement between the talus and the calcaneus in a side-to-side manner. In a further embodiment, the lower member comprises a bony in-growth stem. The bony in-growth stem may be about 45 to 75 mm in length and 7 to 15 mm wide and may be installed in a preformed cavity in the bone that exists from the top of the talus to the distal calcaneus. In yet another embodiment, the bony in-growth stem is secured into the bone, for example, by screws, nails, anchors, or some other means of attachment.
In a further embodiment, the novel ankle replacement system comprises an upper prosthesis body. The upper prosthesis body comprises a tibial prosthesis which further comprises a long stem, approximately 150 mm in length, preferably made of metal. In one embodiment, the long metal stem is covered with bony in-growth scintering.
The present invention also relates a novel surgical procedure for performing TAR which reduces healing time and probability of infection, problems which contribute to the failure rate of currently available TAR systems. The novel surgical procedure comprises introducing ankle prostheses for TAR through the tibia into the ankle. In one embodiment, an exposure is made at the tibial tubercle with an awl. The tibia and tibial plafond are reamed with a tibial reamer inserted through the tibial tubercle exposure. Bony cuts are made in the talus and the end of the tibia. A hole is drilled from the talus into the posterior section of the calcaneus using a talar stem jig. After cartilage has been scraped from the talo-calcaneal joint, a talo-calcaneal bony in-growth metal stem is installed into the drill hole. A talar tray and a plastic dome are placed over the Morse taper on the talo-calcaneal stem and the talar tray is fixed to the talus and calcaneus. A concave tibial dome is placed in the ankle joint. A tibial stem is passed down the tibia to the ankle joint. The end of the tibial stem is locked into the tibial component and the stem is fixed into the tibia with, for example, screws. As part of this procedure, if desired, additional incisions may be made in the foot and/or ankle to allow access to the joint and/or bones of the foot.
In a further embodiment, the top of the talus and end of the tibia may be reamed with a reamer fitted over the end of a rotating shaft which passes through the tibia instead of, or in addition to, cutting the bone. In another embodiment, the metal talar tray may be fixed to the talus and calcaneus with screws. In yet another embodiment, the tibial stem may be fixed to the tibia with screws.
Other objects, advantages, and embodiments of the invention are set forth in part in the description which follows, and in part, will be obvious from this description, or may be learned from the practice of the invention.